After ovulation, ovaries develop enhanced steroidogenic capacity. This requires the availability of cholesterol, a key precursor to steroid hormones. Plasma low and high density lipoproteins (LDL, HDL) are the main source of this sterol for luteal cells of many species. Our goal is to understand how ovarian cells obtain cholesterol from LDL/HDL and to clarify the cellular mechanism underlying this process. Although we have probed the fate of lipoprotein-apoproteins in ovarian cells, virtually nothing is known about the structural bases responsible for the metabolism of LDL/HDL-lipids. Thus, we will develop an autoradiographic method that permits us to trace visually the fate of steryl esters/sterols delivered by LDL/HDL within intact cells. In this way, we will identify the "LDL (HDL) Steryl Ester/Sterol Pathway". Moreover, through biochemical analysis and immunoelectron microscopy, we will test the hypothesis that ovarian hepatic lipase facilitates delivery of HDL-borne steryl esters/sterols to ovarian cells. By studying the uptake of cholesteryl eshers, we will determine if HDL-cholesteryl esters are hydrolyzed by extracellular or intracellular esterases. Agents disrupting microtubules will aid in determining if the cytoskeleton is involved in transporting LDL-derived sterol from lysosomes to mitochondria. We will probe LDL receptor function, including receptor recycling, by using immunocytochemical and biochemical methods. Lastly, we will study regulation of LDL metabolism at a cellular level by determining the effects of tropic hormones on structural aspects of LDL processing and receptor recycling. We will address these issues in the in situ perfused rat ovary and primary cultures of rat and human granulosa cells. We will examine the metabolism of LDL/HDL labeled with: 125I, 3H-cholesteryl linoleate, 3H-cholesteryl linolenyl ether, 3H-cholesterol and colloidal gold. Morphological probes will identify sites of LDL/HDL uptake, enzymes, receptors and the LDL/HDL-steryl ester/sterol pathway. Biochemical studies will provide complementary data on the metabolism of LDL/HDL. The structural and functional information from these studies should clarify how ovarian cells metabolize plasma lipoproteins, thereby acquiring cholesterol needed for steroid hormone synthesis.